The long-term goal of this project is reduction in the pathogenicity of sickle-cell anemia (Hb SS disease) erythrocytes. We are focusing our attention on the red cell membrane, chiefly the external surface (exoface). The rationale is as follows. Although pathology in SS disease is classically described in relation to erythrocyte deformation (sickling), phagocytosis of SS erythrocytes in areas of tissue damage is a pathologic observation of long standing. More recent research suggests that SS erythrocytes tend to adhere to vascular endothelial cells. Both processes might cause significant and potentially dangerous retardation of microcirculatory blood flow. In this project we will characterize and compare exofacial properties of AA, AS, and SS erythrocytes with emphasis on the development of alterations during the cells' in vivo existence. Attempts will be made to distinguish between intracellular and extracellular factors that may influence the development. Parallel studies on the fate of erythrocytes (with identified exofacial characteristics) upon exposure to mononuclear phagocytes and to vascular endothelium will be used as an approach to recognition systems in the human circulation. Exofacial characteristics will be detected by quantitative hemagglutination, radiolabelled antibody and lectin uptake, and single cell techniques. Bearing in mind the fact that alterations at the exoface may well reflect changes that have occurred in other regions of the membrane, we will conduct the following evaluations in attempts to explain our findings at the exoface. Lipid fluidity will be measured by fluorescence polarization of lipid soluble probes using isolated ghosts. Lipid fluidity will also be examined by electron paramagnetic resonance (EPR) technique using intact cells and fatty acid spin probes. Phospholipid rearrangement, which might have a role in altering microviscosity, will be studied using non-penetrating specific chemical probes and enzyme probes. Attempts will be made to correlate the extent of phospholipid rearrangement with altered fluidity. The proposed studies should provide new information on normal processes of erythrocyte senescence and death, most particularly in relation to recognition systems in the circulation. Furthermore information acquired might provide a rational basis for attempts to reduce damage produced by SS erythrocytes in the microcirculation.